Document DE 10 2012 023 819 A1 presents a front sprocket for attachment to a pedal crank of a bicycle, said sprocket being characterized by improved chain guidance in relation to conventional sprockets. The improved guidance characteristics make it possible, to dispense with additional chain guides when using a single such sprocket on a pedal crank of a bicycle. This is the case even if no chain guide of a chain derailleur is provided. This characteristic may be an advantage in the case of bicycles for off-road use and in the case of which, owing to unevenness in the terrain and in the event of intense steering movements, the chain has a tendency to jump off the sprocket. The improved guidance characteristics are due at least partially to thick and thin teeth of the sprocket which are arranged in alternating fashion in the circumferential direction, as viewed in the axial direction of the pedal crank.
Furthermore, said teeth may be of particularly long form in a radial direction, wherein the tooth spaces may be formed so as to be only insignificantly larger in a circumferential direction than the chain rollers received therein. Furthermore, it is possible to provide free spaces in order to provide space for the inner links of the chain, which project relative to the chain rollers.
In the case of said prior art, only one of said sprockets is provided on a pedal crank, such that a front derailleur can be dispensed with. The need for the roller-type drive chain to be changed over to an adjacent sprocket in the load strand, which normally poses high demands due to chain tension forces prevailing in the load strand, is thus eliminated. The stated sprockets are not suitable for use on a rear-wheel hub, because the exceptionally good chain guidance characteristics oppose a changeover or shift to an adjacent sprocket.
Similar sprocket arrangements are also known from US 2014/0338494 A1 and DE 10 2014 019 528 A1.
The gearshift processes and associated requirements at multi-sprocket arrangements of a pedal crank, however, differ significantly from those of a multi-sprocket arrangement for a rear wheel hub of a bicycle. In the case of a driving sprocket (at the pedal crank), the chain roller is received in each case by the load flank of the sprocket. The drive direction defines that the gearshift process must be performed in the load strand. In the case of a driven sprocket, for example a pinion of a pinion cassette mounted on a bicycle rear wheel, the chain roller runs in on or close to the run-in flank, in the idle strand of the drive. The chain guidance is performed by the gearshift mechanism toothed roller, such that the run-in situation onto the respective sprocket does not involve significant skewed running. This gives rise to completely different demands being placed on the gearshift, and on the guidance of the chain therefor, for a rear sprocket (pinion) on the rear wheel of a bicycle as opposed to a front sprocket on the pedal crank of a bicycle.
It is an object of the present invention to provide a multi-sprocket arrangement for a rear wheel hub of a bicycle, which multi-sprocket arrangement exhibits improved shifting characteristics, in particular during a shift to sprockets of relatively small diameter and during gearshift processes with large differences in numbers of teeth. Furthermore, it is the intention to improve the skewed-running characteristics and reduce wear.